In the industry manufacturing various kinds of structural members by making use of welding, efforts are being made to improve operation efficiency by increasing the speed of welding or introducing a high-deposition welding process. In order to further improve the efficiency, some welding firms have introduced an integrated welding torch which can supply two weld wires, or such a welding method which uses a single-electrode welding torch for two pieces disposed in proximity to each other. They are referred to as the tandem arc welding.
A tandem arc welding system performs a certain specific action at a certain specific speed and controls the welding process to accomplish a welding operation. An operation program is provided on an assumption that the two electrodes, including the weld wires which are supplied penetrating through respective electrodes, are disposed substantially on welding line in a certain welding section, in front and the rear orientation.
Now, a tandem arc welding device is described in its outline formation and operation, referring to FIG. 1. FIG. 1 shows the outline structure of a tandem arc welding device having an integrated 2-electrode welding torch. Integrated 2-electrode welding torch 50 is attached on a welding robot manipulator or the like working gear, not shown, and travels on the surface of welding object 60 along a certain specific welding line. A device for putting a robot manipulator, etc. into action is coupled with control unit 20. Control unit 20 is connected with two welders, 30 and 40. Respective welders 30 and 40 are provided with a weld wire feeder, not shown, for feeding a weld wire, not shown, to welding torch 60; namely, the torch is supplied with two weld wires. Within welding torch 50, each of the two weld wires is delivered penetrating through an electrode tip, not shown. The electrode tips are connected with output terminals of welder 30 and welder 40 via power cable 31 and power cable 42, respectively. Electric powers from welder 30 and welder 40 are supplied to respective weld wires. Welding object 60 is connected to the ground terminals of welder 30 and welder 40 by way of grounding cable 32 and grounding cable 41. The arcs between the weld wires and welding object 60 constitute circuits for the welding currents.
Control unit 20 houses an operation program and welding conditions, and controls a welding robot manipulator, etc. by transferring from time to time the instructions and parameters to welder 30 and welder 40 via control line 33 and control line 43 in accordance with the operation program. Welder 30 and welder 40 control their own weld wire feeders so that the weld wires are supplied for certain specified quantities corresponding to the parameters instructed by control unit 20. In this way, a tandem arc welding device implements a certain specific welding operation on welding object 60 at a certain specified place.
Now in the following, description is made on how a tandem arc welding is implemented, with reference to FIG. 2. FIG. 2 illustrates a scene where a tandem arc welding is being carried out with an integrated 2-electrode welding torch (ref. FIG. 1), in the direction from the right to the left. The terminologies here, “fore-going” means that which is proceeding ahead along a welding line, while “hind-going” means that which is going in chase of the “fore-going”.
Reference is made to FIG. 2, there are two electrode tips, fore-going electrode tip 51 and hind-going electrode tip 52, disposed at a certain specific electrode-to-electrode distance within the inside of nozzle 58 of integrated 2-electrode welding torch 50. Fore-going electrode tip 51 is supplied with fore-going weld wire 53, while hind-going electrode tip 52 is supplied with hind-going weld wire 54.
Fore-going weld wire 53 obtains electric power from a welding power supply source for fore-going electrode, not shown, via fore-going electrode tip 51, and generates fore-going arc 55 between fore-going wire 53 and welding object 60. The heat of arcing melts fore-going wire 53 and welding object 60 to supply molten pool 61 with the molten metals. At the same time, hind-going weld wire 54 obtains electric power from a welding power supply source for hind going electrode, not shown, via hind-going electrode tip 52, and generates hind-going arc 56 between hind-going wire 54 and welding object 60. The heat of arcing melts hind-going wire 54 and welding object 60 to supply molten pool 61 with molten metals. Fore-going wire 53 and hind-going wire 54 are delivered continuously while integrated 2-electrode welding torch 50 travels at a certain specific speed. Molten metal pool 61 moves forward and weld bead 62 is formed behind it; thus, a welding operation takes place. Fore-going electrode tip 51 (or hind-going electrode tip 52) and fore-going weld wire 53 (or hind-going weld wire 54) are referred to as the electrode, altogether.
In a tandem arc welding, the fore-going electrode and the hind-going electrode have, respectively, their own specific roles. For example; in FIG. 2, the molten metals in molten pool 61 formed by fore-going arc 55 which is generated by fore-going wire 53 tends to flow backward under the influence of arcing power of fore-going arc 55. Meanwhile, the arcing power of hind-going arc 56 which is generated by hind-going wire 54 pushes it back. Molten pool 61 stands on a balance between the two powers. Besides the above-described, each of the electrodes plays specific role of its own for the weld penetration and the shaping of weld bead 62. Thus, the two electrodes are not playing the same functions. So, welder 30 and welder 40 need to be provided with different parameters of welding conditions in carrying out a welding.
Arrow mark 59 in FIG. 2 indicates, for example, a welding operation conducted in the forward direction, viz. a welding proceeding from the right to the left. On the other hand, if a welding is made along the reverse direction, the direction is opposite to that indicated by arrow mark 59, or the direction from the left to the right in FIG. 2. Since parameters to be sent to fore-going welder 30 (or welder 40) are different from those to be sent to hind-going welder 40 (or welder 30), the welding condition parameters for welder 30 and those for welder 40 have to be exchanged when making a welding the reverse direction. Therefore, when controlling the welding conditions in a conventional tandem arc welding device, the program is required to include a certain procedure for specifying which of the two will be the fore-going. As a practical example, there can be four modes: namely, a tandem welding mode which uses both of welders 30 and 40, with one of which specified as fore-going electrode; that which uses the other welder as the fore-going; and a single welding mode which uses only one of the welders 30 and 40 alone. In providing an operation program for a tandem arc welding, there has been a generally-used technique of specifying the modes. Such conventional technique used for tandem arc welding is disclosed in, for example, Patent Document 1 described later.
As described in the above, the conventional tandem arc welding devices has a restriction that the welding conditions need to be provided considering which of electrodes 50a or 50b will be the fore-going, and the operation program has to include such descriptions in it. This means that both the operation program for welding object 60 and the welding conditions described in there are dependent on a reality which one of the electrodes is the fore-going. Therefore, program making staff have always keep in mind which of the electrodes is going ahead of the other. Furthermore, this has another inconvenience that re-use of an operation program and welding conditions contained in there for other welding object 60 is limited.
[Patent Document 1]
Japanese Patent Unexamined Publication No. 2003-053535